In hammermills and other forms of devices for treating materials, contact elements such as contact tips are caused to move into impact engagement with rocks or other materials to be treated so as to crush the materials. It is necessary that the contact elements be securely and reliably supported and since they are subjected to severe wear, it is also necessary that they be replaceable. In hammermills of the prior art, the contact tips have been supported at the ends of pivotal support arms through tongue-and-groove connections permitting relative slidable movement of the contact tips for installation thereof. Various forms of means have been provided for use after installation for preventing relative slidable movement away from the installed position. In some cases, suitable keys have been driven in, sometimes with a wedge engagement and in others, locking plates have been welded in place.
Such arrangements have been generally satisfactory and certain problems therewith and potentialities for improvements thereof have not been recognized in the prior art. In particular, the installation and removal of the contact tips has presented some degree of difficulty and has been time-consuming. Also, there has oftentimes been some degree of freedom of movement of the contact tips relative to the support arms, with corresponding problems connected therewith.